A research program is proposed which has as its primary objective the development of synthetically useful methodologies derived primarily from the electrophilic metal Pi- complexes (propargyl)Co-2(CO)6+ (1), (allyl)Fe(CO)-4+ (2), and (diene)Co(CO)L-3+ (3). Previous work has established the facile, regioselective coupling of numerous carbon nucleophiles with the complexes 1 and several derivatives. This proposal seeks to examine the stereochemistry and to utilize new variations of these reactions in the synthesis of selected, representative biologically active compounds and key intermediates including marine acetylenes, macrocyclic antibiotics, guiane and pseudoguiane sesquiterpenes (cytotoxic, anti-tumor), and steroids with modified side chains (sex hormones, anti-tumor agents, vitamin metabolites). Following preliminary studies of the reactions of 2 with selected nucleophiles which point towards generally high regio- and stereoselective couplings, iron-catalyzed allylic alkylation has recently been discovered. Future efforts will focus on: 1) defining the scope of these iron catalyzed reactions with respect to nucleophiles, substrates, and their influence on regio- and stereoselectivity; 2) comparing these reactions with their stoichiometric counterparts, those of 2 and (n-2-allylX)Fe(CO)4; and 3) examining reactions with allyl nuleophiles as a regio- and stereo- selective isoprenylogation methodology. Finally, fundamental "ground-breaking" studies of the preparation and reactivity of electrophilic n-4-diene complexes, 3 will be conducted. Chief questions of interest include the regio- and stereoselectivity of attack on 3 by nucleophiles. Development of synthetically useful methodologies from these studies may have future applicability in the construction of complex natural products.